Three DES-induced hamster tumors: pars intermedia adenoma, epididymal head adenoma, and uterine carcinosarcoma, are being studied electron microscopically, immunologically for HaLV gs antigen, and electrophoretically for G-6-PD isoenzymes. Initial samples of each tested for HaLV gs antigen showed low to very low activity. Electron micrographs of the tumors have not revealed at this time any visible C- type RNA particles. A first serial passage of a DES-induced renal tumor appears similar to nephroblastomas. This tumor is now being passed in DES- and non DES- treated hosts to determine if it is indeed estrogen-dependent. Inclusion material (intranuclear and intracytoplasmic) has been observed in H & E stained collagen-coated coverslip cultures of estrogen/androgen-induced scent gland tumors. These cultures are now being processed electron microscopically to determine the fine structure of the inclusion material. Work is continuing to separate out the cell types of the scent gland tumor and grow each type in host animals, studying the individual effects of estrogen and androgen. The inhibitory effect of antiviral and antiestrogen agents on the above tumors is being studied.